A combination or combi boiler is both a high efficiency water heater and a central heating boiler in a single compact unit.

Combi boilers heat water directly from the mains when you turn on a tap, so you won't need a hot water storage cylinder or a cold water storage tank in the roof space. They are also very cost-effective and energy-efficient as water is heated instantly rather thank being heated and then stored in a cylinder.

An added benefit is that hot water is delivered at mains pressure, which means that you could get a powerful shower without the need for a separate pump.